Which of the following represents the correct reactivity order for both $SN^1$ and $SN^2$ mechanisms?

The reaction of chloroform with concentrated $HNO_3$ yields ........

The mechanism of $S_{N}1$ reaction is given as:
$R-X$ $\rightarrow R^{\oplus} X^{\ominus}$ $\rightarrow R^{\oplus} | X^{\ominus}$ $\xrightarrow{Y^{\ominus}} R-Y + X^{\ominus}$
(Ion pair) (Solvent separated ion pair)
$A$ student writes general characteristics based on the given mechanism as:
$(a)$ The reaction is favoured by weak nucleophiles
$(b)$ $R^{\oplus}$ would be easily formed if the substituents are bulky
$(c)$ The reaction is accompanied by racemization
$(d)$ The reaction is favoured by non-polar solvents.
Which observations are correct?

The reaction of $CH_3CD_2CHBr-CH_2CD_3$ with alc. $KOH$ yields:

What are $X$ and $Y$ in the following reaction sequence?

In the reaction shown,the major product obtained is: